mediainfo: fix build with clang 5.1

Small fix to fix compilation under current shipping XCode command-line
tools.

These changes are also applied upstream
(http://sourceforge.net/p/mediainfo/code/6167/) but have not made it
into a proper release yet.

Fixes #27393.
Closes #27851.

Signed-off-by: Misty De Meo <mistydemeo@gmail.com>